This invention relates to means for preventing the automatic restart of an electric motor, such as the drive motor for a power tool or other motor application, upon inadvertent deenergization of the motor thereby to reduce the danger of injury to the operator of the power tool or damage to the tool or to the work as may be caused by the unexpected restarting of the motor.
In certain motor applications, particularly in drive motors for power tools and the like, a danger to the operator or user of the power tool may be present if the tool would unexpectedly start up after an unintended stoppage of the tool. For example, in a table saw, the drive motor normally continues to operate once it has been energized until it is selectively shut down (i.e., it does not use a trigger switch which must be held open to energize the motor). However, in the event the power supply to the drive motor is inadvertently terminated and then is subsequently restored, the power tool may unexpectedly start up upon restoration of the power causing injury to the tool operator or damage to the tool or work piece. More specifically, if the power lead for the tool would inadvertently become unplugged from a wall socket or if the power to the building would be temporarily interrupted due to an outage, replugging the power lead into the wall socket or restoration of the power could restart the drive motor.
Reference may be made to U.S. Pat. No. 3,293,388 granted to J. L. Slonneger on Dec. 20, 1966 for certain background information relevant to the present invention.